William burnett



W. BURNETT.

Pressure Gage.

No. 33,062. Patented Aug. 1i3',-1861.

WILLIAM BURNETT,. OF BOSTON, MASSACHUSETTS, ASSIGNOR ROBERT BURNETT, OF NEW YORK, N. Y.

BRESSURE-GAGE.

Specification of. Letters PatentNo. 38,062,.dated August. 13, 18,61.

To all whom it may concern:

Be it known that I,.'WILLIAM BURNETT, of Boston, inthe'county of Su-flollnin the State of Massachusetts, have invented certain improvements in, Pressure; Gages or Indicators; and I do hereby declare that the following is a full and exact description thereof, reference being had to the accompanying drawings, and to letters of reference marked thereon, the same letters referring to like partswhere shown in; both figures.

The nature of my invention consists in a novel mode of introducing the pressure into the cavity behind the elastic plate, in gages in which such means are employed to obtain a first motion, and further consists in. a novel arrangement-20f mechanism by which the first motion in pressure gages maybe transmitted to the index hand or pointer.

Tolenableothers skilled in the art to make and use my invention, I will proceed to de scribe its construction and operation, reference being; had; to the accompanying drawings, making part of this specification.

A circular metallic case (A) of proper depth to receive the working parts, is provided with aback of sufficientthickness to resist without injury, any pressure to which the gage may be; subjected. In this latteris provideda cavity- (B) of suitable depth and diameter, which, when covered by the elastic plate (G) ,forms the chamber into which the pressure-to. be measured is introduced The elastic pla-tel (C); is secured in its place by means of a metallic ring (D) ;0f proper dimensions, which is held firmly down on the top of the plate by means ofscrews (E) which pass through. the metallic ring (D), and elastic plate (0), and are screwed. into the back ofthe case. One end of a rigid bar or arm (F); isfirmly bolted to the elastic plate (C) at a point considerably removed from its center, as shown in. thedrawing,

and at that part: of its surface which as sumes, when pressure is admitted beneath the plate, the steepest angle when considered relatively to the plane represented, by the surface of the plate when in a state of rest or equilibrium. From a short standard (G4), whichis either cast upon or screwed into the metallic ring (D), is suspended, by means of a. properly fitted pin, a vibrating bar. (H), which is connected by a. link (J) to thefree end. of the rigid arm (F), before (lQSGI'lbBCh' In fitting the vibrating bar into the standard (G), a little side oscillation is permitted. to the lower end of the Vibrating bar, to give freedom to its action against a spiral shaft (L), which carries upon its outer end the index hand or pointer A flange projection (K) of nearly triangular form, is cast upon the metallic ring (D), and forms a, hearing or step for the inner end of. the spiral shaft This projecting fian 'e (K) is sufficiently far removed from the elastic plate (G) to allow of the free working of the latterwhen subjected to pressure. A bracket (N), which is secured. to the projecting flange (K) by screws (0), furnishes a bearing for the outer end of the spiral shaft. Cast uponthe metallic ring (D) are three projections (P). to whichv is secured, by screws (p), the index plate (Q). A screw ring (it) holds in. its place the circular glass plate (S) which protects the internal mechanism from dust or injury. Upon the metallic ring (D) is also cast a suitable enlargement or boss (T), to increase its thickness at this particular place for the purpose of having suiiicientmaterial. into which may be screwed the pipe (U), through which the pressure is. introduced. A hole sufficiently large toreceive the pipe (U), is drilled into the edge of the ring at this place,aad another hole (V) of smaller diameter, is then drilled. into the back of, the ring, so as to in.- tersect the first; the plate (C) is provided with an opening through. it, in continuation of this passage (V), which communicates, by means of a grooveor channel (X) below the elastic plate,with the pressure chamber (B).

By this. arrangement for introducing the pressure, I am. enabled to, employ an elastic plate the full size of the interior of the case, and at the same time to secure a flush back tothe gage, renderingit easy of attachment toany flat surface, and avoiding the unsightly and inconvenient projections on the back of the case, whichwould, be otherwise necessary for. the. introduction of the pressure, Where so. large an elastic plate is employed;

The seat upon, which the elastic plate rests is provided withia suitable packing to prevent leakage, and a thin, packing is also in tro'duced between the ring and the I elastic plate, at that point where the pressure is introduced through the elastic plate into the channel leading into the pres sure chamber. The metallic ring (D) may be cast as a flange on the inside of the case (A), and formthe seat for the elastic plate, which, in that case, would be inserted from behind, the thick portion of the back of the case (A) being made in a separate piece for this purpose; the pressure, however, would still be introduced into the ring (D) in front of the elastic plate, thence through the plate itself, into the channel behind the plate, communicating with the pressure chamber. But I prefer the arrangement of making the ring (D) separate from the case, as represented. I

One side of the enlarged central portion of the shaft (L), between its bearings, is cut spirally, nearly throughout its whole length,

by filing or other means, and when finished, would present, approximately, a semicylindrical cross section. The spiral surface thus formed, I make of a diminishing pitch, that is to say, of a coarser pitch at the end of the shaft nearest the elastic. plate, diminishing the same toward the outer end of the shaft in the same ratio in which motion is communicated to the vibrating bar (H), through the action of the pressure, from minimum to maximum, on the elastic plate. The object of this is to secure uniform divisions on the index plate for equal increments of pressure, which would not result unless some such expedient were adopted.

Used as a vacuum gage, the vibrating bar (H) would commence its motion from the outer end of the shaft, as the movement of the elastic plate would be, in this case, reversed, and the spiral shaft must also be reversed so that the coarser pitch is at the outer end, the same diminishing as it ap proaches the end nearest the elastic plate, for the same reasons stated above. The spiral shaft (L) has another important peculiarity of form, which arises from the fact that the spiral surface has been formed with direct reference to the point of suspension of the vibrating bar (H), with the view of securing between the working face of the vibrating bar and the spiral face of the shaft, a proper fit and contact throughout the entire movement; which would not be the case unless the various angles assumed by the vibrating bar throughout its motion were thus accommodated. Thus, a shaft of similar transverse section to that described, the spiral surface of which had not been formed with reference to the point of suspension of a bar by which it was to be driven, although such vibrating bar might be fitted properly to its spiral surface at the center of the shaft, it would not fit equally well at the ends. At one end, on account of the vibrating bar having assumedan angle more co incident with the direction of the spiral, it would be quite loose, permitting uncontrolledmotion of the index pointer, within certain limits: At the other end, the vibrating bar having in this case assumed an angle less coincident with the direction of the spiral, it would be forced out of proper contact.

The end of the vibrating bar which works against the spiral surface of the shaft, is rounded on the working face, and this end of the bar, as well as the shaft itself, both of which are made of steel, is hardened by tempering. The bracket (N) which supports the outer end of the spiral shaft, is placed so near to the back of the vibrating bar (H), that, although suflicient clearance is allowed for free action, it cannot in any case, recede so far from its proper contact with the spiral surface, as to permit indications'very materially differing from the true pressure. But in addition to having provided this safeguard, the vibrating arm H) is furnished with a light flat spring Y), one end of which is securely united to it, at a proper distance above its point of contact with the shaft, the other end reaching down to the end of the vibrating bar, and embracing the shaft in such a manner as to. draw the vibrating bar nicely and delicately into its proper seat and contact with the spiral surface of the shaft. This spring (Y) may be attached to the back of the bar (H), its lower end bearing against the bracket (N), but I prefer the application represented in the drawing. I sometimes apply a light spiral spring (Z), stretched between the vibrating bar (H) and the rigid arm (F), for the purpose of taking up any slack in the pivots, which may result from wear.

The operation of the gage is as follows; The pressure is admitted into the chamber (B) behind the elastic plate (C), by means of a pipe (U) and passages (V X) as represented. 'The elastic plate, bearing the rigid arms (F), is bulged outward, throwing the top of the arm forward. This latter movement is communicated by means of the link (J attached, to the vibrating bar (H), the lower end of which being engaged in the spiral shaft (L) causes it to revolve, and indicate the pressure, by means of the pointer (M) carried on its outer'end, and working over the index plate.

I do not claim to have invented elastic metallic plates to be used in pressure gages, for the purpose of deriving motion there from upon the application of pressure, as I am aware they are now used, and well known. Neither do I here claim the mode described of obtaining an enlarged first motion, through the agency of an arm affixed to the elastic plate at a point removed from its center, as this the subject of a patent now about to issue to Robert Burnett, as my assignee. Neither do I claim broadly the use of spiral or screw shafts in pressure gages, to give motion to an index hand or pointer, as I am aware they have been used of various forms.

That I claim as my invention, and desire to secure by Letters Patent, is

1. The mode herein described, of admitting the pressure into the chamber behind the elastic plate, viz :-by first introducing the pressure into the ring in front of the elastic plate, thence through the plate itself, into a channel communicating with the pressure chamber, substantially in the manner and for the purpose herein specified.

2. The use of a spiral shaft, to give motion to a pointer, when the same is constructed by cutting away spirally, one half, of the material of the shaft, so as to present, approximately, in its transverse section, a semi-cylindrical body, substantially as herein described, by which I am enabled to secure a working face equal to the whole diameter of the shaft, while suficient stiffness is retained to present no obstacle to its manufacture, and to insure permanency of character.

3. Operating the spiral shaft, giving 1110- tion to a pointer, by means of a vibrating bar which is forced into proper contact with the spiral surface, by a spring attached to the bar and operating transversely t0 the axis of the shaft, substantially as described.

l. Providing a guard to prevent the vibrating bar, which operates the spiral shaft, from receding so far from its proper contact with the spiral surface as to permit indications very materially differing from the true pressure,by placing an unyielding body near to the back of the vibrating arm, and parallel to the axis of the shaft, substantially as described.

5. A screw or spiral shaft of diminishing pitch, to give motion to a pointer, substantially as herein described.

6. Forming the spiral surface of a shaft, employed to give motion to a pointer, with a reference to the point of suspension of a vibrating bar Working in contact with said spiral surface,-by which arrangement of the two I secure a proper working contact throughout the length of the shaft, and in all positions which are assumed by the vibrating bar, substantiallyin the manner and for the purpose herein specified.

WM. BURNETT. lVitn esses CHAS. B. STEWART, J. T. BALL. 

